The differences between the production of printing forms in accordance with the "indirect stencil method" and in accordance with the "direct stencil method" are explained in U.S. Pat. No. 4,214,522, which also describes and illustrates an arrangement for producing or treating printing form (stencils) intended for use in silk screen printers.
This method is based on the application of a light sensitive coating to a cloth stretched in a supporting frame, and processing the coating with light so as to effect an image transfer corresponding to the desired printing pattern.
The cloth is intended to be treated with liquid, i.e., water, such as either to clean the cloth or develop the pattern. To this end the arrangement includes at least two pipes which have mutually opposing nozzles and which are intended to co-operate with a holder in a manner such that one of said two pipes will pass over the rear side of the cloth while the other pipe will pass over the other side of the cloth with the nozzles facing one another.
For the purpose of producing printing forms in accordance with the "direct stencil method" it is known to produce such forms manually and in sequence by providing a cloth stretched in a printing frame with a light-sensitive coating, permitting the coating to dry, exposing an image corresponding to the desired printing pattern on the light-sensitive coating, with the aid of a camera arrangement including, inter alia, a light emitting means, developing the printing pattern and fixating and drying the coating surrounding said pattern.
Considering that large posters, placards or the like are composed from a multiple of mutually adjacent part images, e.g. 8 images, which form the total image, and considering that four different printing forms are required for each part image in a four-colour printing process, one for each colour, the number of printing forms required to produce a single poster will be quite considerable.
Since large posters are normally produced in limited numbers, an obvious requirement is to achieve a high rate of manufacture of the printing forms, in order to keep down the total manufacturing costs.
Consequently, in the case of printers of average size it is not unusual to fully employ several workmen with the task of producing the requisite printing forms, and even with the task of touching-up the printing pattern on the cloth in order to rectify defects caused by the influence of undesirable dust particles on the printing form pattern.